In recent years, renewable energy has been developed to take measures against global warming. For example, practical application of floating offshore wind power generation has been promoted in which power is transmitted from wind turbines as offshore floating facilities.
To transmit power from offshore floating facilities, undersea cables are used. The undersea cables have the following structure. Three power line cores are twisted together for three-phase alternating-current power transmission, and wire armor lines are provided on an outer periphery of the cores to support the cable load. An outermost portion is coated with a plastic layer by extrusion coating to prevent external damages.
Examples of such undersea cables include an undersea cable in which a wire armor member is provided on an outer periphery of a linear aggregated member. The linear aggregated member is formed by twisting cable cores and twist reinforcing wires together in one direction. The wire armor member is formed by twisting wire armor lines together in a direction that is opposite to the direction in which the cable cores and the twist reinforcing wires are twisted together. Accordingly, when the wire armor member is provided on the outer periphery of the linear aggregated member, the twisting torque acting on the linear aggregated member and the wire armor member is cancelled to balance the torque (Patent Document 1).